1. Field of the Invention
The present invention relates to a method of analyzing an iron concentration of a boron-doped p-type silicon wafer. More particularly, the present invention relates to an analysis method permitting the obtaining with high precision of the iron concentration of a boron-doped p-type silicon wafer by the surface photovoltage method (SPV method).
The present invention further relates to a method of manufacturing a boron-doped p-type silicon wafer with reduced iron contamination, and a silicon wafer with a written quality guarantee obtained based on the above analysis method.
2. Discussion of the Background
The heavy metal contamination of a silicon wafer negatively affects the device characteristics of the finished product. In particular, even a trace quantity of Fe contamination in a wafer functions as a recombination center, causing an increase in the amount of reverse leakage at pn junctions in devices and causing the failure of memory refreshment and the like in memory elements. Accordingly, it is required to accurately determine the level of Fe contamination of wafers for process management.
In boron-doped p-type silicon, electrostatic forces cause the Fe to bond with the boron, forming a Fe—B pair. The surface photovoltage method (SPV method), which utilizes a change in the measurement value of a minority carrier diffusion length before and after the separation of the Fe—B pair, is widely employed as a method of quantifying the concentration of iron in boron-doped p-type silicon wafers (for example, see Japanese Unexamined Patent Publication (KOKAI) No. 2005-64054, Japanese Unexamined Patent Publication (KOKAI) No. 2005-317562 as well as English language family member US2006/063324A1 and U.S. Pat. No. 7,141,992, which are expressly incorporated herein by reference in their entirety).
The SPV method is currently widely employed as a process management method and quality assurance method to stably provide high-quality boron-doped p-type silicon wafers with little iron contamination. The SPV method is a good method that permits automated measurement without requiring a high level of skill in the manner of chemical analysis. However, there is a need to further raise the analysis precision to provide higher quality silicon wafers.